This investigation will examine the role of membrane lipid metabolism in the regulation of parathyroid cell function. Collagenase-dispersed bovine parathyroid cells will be used throughout. The studies will focus initially on the role of calcium-induced changes in phosphatidylinositol formation and the resultant effects on parathyroid hormone and parathyroid secretory protein secretion. The approach will be to assess the rate of radiolabeled phosphate and glycerol incorporation into phosphatidylinositol and related metabolites. Lipids will be separated by thin layer chromatography and radiolabel content quantitated by autoradiography followed by densitometry. The de novo synthesis of phosphatidylinositol as opposed to flux through the "PI-cycle" will be determined and correlated with protein secretion. Subcellular fractionation will be used in order to identify the cellular locus of altered lipid metabolism in relation to protein secretory mechanisms. The role of calcium dependent phospholipase C or A2 will be assessed and the effect of calcium on the metabolism of the liberated arachidonate through lipoxygenase and cyclooxygenase pathways will be determined. Lipid metabolites will be isolated and incubated with parathyroid cells in order to determine their individual effects on hormone secretion. The effect of glycolytic or tricarboxylic acid cycle substrates on hormone secretion will be examined in order to determine the preferred substrate(s) of parathyroid cells for optimum activity. The influence of calcium on cellular metabolism will be determined by the evolution of radioactive CO2 from specifically labeled substrates. In addition, the effect of calcium on parathyroid cell membrane permeability and substrate transport will be assessed by the uptake of non-metabolizable substrate analogues to assess the contribution of calcium on uptake vs utilization of substrates. The influence of calcium on membrane bioelectric properties will be determined and the contribution of calcium flux at various calcium concentrations through membrane channels in relation to hormone secretion will be assessed. The molecular properties of the calcium ion sensing site of parathyroid cells that controls membrane activity will be determined through quantitative effects of the different group IIA metal ions and various lanthanides on transport and secretion. These results will be integrated to describe the effects of calcium on general membrane function that result in changes of hormone secretion.